1. Field of the Invention
The present invention generally relates to a hybrid vehicle drive control system for a hybrid vehicle having an electric drive (EV) mode in which a drive wheel is solely driven by a motor/generator and a hybrid drive (HEV) mode in which the drive wheel is driven by an engine and the motor/generator, or the engine only. More particularly, the present invention relates to a hybrid vehicle drive control system that is configured to control a torque transfer capacity of a clutch to start the engine from the torque of the when motor/generator switching to the latter the hybrid drive (HEV) mode from the electric drive (EV) mode.
2. Background Information
Various configurations have been proposed for hybrid vehicle drive control systems to be used in hybrid vehicles. One such hybrid drive system is presented in Japanese Laid-Open Patent Publication No. 11-082260. The hybrid vehicle drive control system presented in Japanese Laid-Open Patent Publication No. 11-082260 has a motor/generator arranged between an engine and a transmission so as to be coupled to a shaft that directs the rotation of the engine to the transmission. A first clutch is arranged for operatively connecting and disconnecting the engine to and from the motor/generator, while a second clutch is arranged for operatively connecting and disconnecting the motor/generator to and from the output shaft of the transmission. The second clutch is provided to replace a conventional torque converter that is used in a conventional automatic transmission.
A hybrid vehicle equipped with a hybrid vehicle drive system like that just described can be put into an electric drive (EV) mode in which the vehicle travels solely by means of power from the motor/generator by disconnecting the first clutch and connecting the second clutch. Such a hybrid vehicle can also be put into a hybrid drive (HEV) mode in which the vehicle travels using power from both the engine and the motor/generator by connecting both the first clutch and the second clutch. Accordingly, the second clutch is a clutch that directs the drive power from both the engine and the motor/generator to the drive wheel. In the electric drive (EV) mode, the motive power of the engine is of course not needed, and therefore the engine is stopped.
However, in such a hybrid vehicle, the output of the engine during travel in the HEV mode is needed. Also when switching from the electric drive (EV) mode to the hybrid drive (HEV) mode, it is necessary to perform the drive mode switching while starting up the engine. When switching drive modes and simultaneously starting up the engine, the switching of the drive mode from the electric drive (EV) mode to the hybrid drive (HEV) mode is conventionally performed by engaging the first clutch, which is disposed between the engine and the motor/generator, and then starting the engine by cranking the engine from a stopped state via the drag torque of the first clutch, as disclosed in Japanese Laid-Open Patent Publication No. 11-082260.
Furthermore, it also proposed in this conventional technology to temporarily disengage the second clutch, which is disposed between the motor/generator and the transmission, when starting the engine, and then engaging of the first clutch so as to prevent shocks caused by the transmission to the drive wheels due to, for example, torque fluctuations that arise when engaging the first clutch, as well as torque fluctuations that include engine torque overshoot and polarity inversion at engine startup.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved hybrid vehicle drive control system. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.